Christopher Manning left Serco Australia in May 2012 as their managing director of immigration detention centres.

He was hired by G4S in September, shortly before the company secured the contract to run the Manus Island centre in Papua New Guinea.

Mr Manning was tasked with managing the project, and helped G4S in its bid for the job.

But Serco took legal action against him in the ACT Supreme Court, arguing he breached a contract banning him from working for a rival in Australia for a year.

Mr Manning’s legal team argued their client honoured the terms of the agreement.

In October the contractor sought an interim injunction banning Mr Manning from working for G4S until the court case was resolved.

Lawyers for Serco told Master David Harper their former employee had detailed knowledge of confidential information and a tight relationship with the Department of Immigration and Citizenship.

They argued his work with Serco's rivals had the capacity to damage its commercial operations and relationship with the department.

But Master Harper on Wednesday said the Supreme Court had since offered an expedited hearing date, and granting the injunction would case “immediate negative effect” to G4S.

The master said while the rival contractor wasn’t a party to the case there was an “irresistible inference” they were legally backing him.

“Nevertheless, there is no basis for a conclusion that G4S has enticed the defendant away from the plaintiff, or that G4S has any intention of utilising the defendant’s services to enhance its relationship with the [government or DIAC],” he said.

“There is no basis for a finding which goes any further than that G4S sees the plaintiff [Mr Manning] as the best available candidate to manage the Manus Island operation.”

He refused the injunction, and ordered Serco to pay Mr Manning’s legal costs for the application.

The decision comes after the first groups of asylum seekers arrived at the Papua New Guinean facility integral to Australia’s off-shore processing policy.